This invention relates to an improved process for the isomerization of dichlorobutenes, wherein formation of solids and high boiling byproducts is inhibited.
It is known to isomerize 1,4-dichlorobutene-2 to 3,4-dichlorobutene-1, or vice versa, in the presence of a copper salt, e.g., in the presence of a complex of a copper salt with a quaternary ammonium compound, as described in U.S. Pat. No. 3,819,730 to Nakata et al. 1,4-Dichlorobutene-2 is a valuable intermediate in the manufacture of certain important polyamides, such as nylon 66; while 3,4-dichlorobutene-1 is an equally valuable intermediate in the manufacture of chloroprene, which is the basic monomer in the manufacture of a class of important synthetic rubbers known as the neoprenes. In the Nakata et al. process, substantially pure 1,4-dichlorobutene-2 or 3,4-dichlorobutene-1, or a mixture thereof is fed to a constant boiling reactor operating under reduced pressure and containing the cuprous chloride/quaternary ammonium compound catalyst; the isomerized dichlorobutene compound is taken off as a vapor, then condensed and fractionated to yield substantially pure 3,4- and 1,4-dichlorobutene, respectively. There are known other processes based on a cuprous compound catalyst or complexes of cuprous chloride with amines, amides, or nitriles.
The above processes suffer to a greater or lesser degree from side reactions, which lead to the formation of high boiling liquids or of solids, likely containing oligomerized and/or polymerized materials, which eventually cause clogging of the reactor, reduce the efficiency of heat exchange in the reactor, and naturally reduce the yield of isomerized dichlorobutene.
It is, therefore, the objective of this invention to provide an improvement in the dichlorobutene isomerization process wherein those side reactions would be substantially inhibited.